1. Field
The present invention relates to a semiconductor light emitting diode and a method of manufacturing the same, and more particularly, to a semiconductor light emitting diode including an ohmic electrode structure on a semiconductor layer of a light emitting structure to connect an external power source and a method of manufacturing the same.
2. Discussion of the Background
A semiconductor light emitting diode (LED) has a long lifespan, is small and lightweight, shows strong directivity of light, and can be driven at low voltage. In addition, a semiconductor light emitting diode (LED) is resistant to impact and vibration, does not require preheating and a complex driving circuit, and may be packaged in various forms. In particular, a nitride semiconductor light emitting diode allows an optical output having a wide wavelength band ranging from an ultraviolet region to a blue/red region due to a large energy band gap and has been being spotlighted to realize high efficiency and high output due to excellent physical/chemical stability thereof. Such a nitride semiconductor light emitting diode can be combined with existing red and green light emitting diodes to emit white light, and it is considered that the nitride semiconductor light emitting diodes will replace existing white light sources, such as incandescent, fluorescent, and mercury lamps, in the near future.
However, current nitride semiconductor light emitting diodes are not satisfactory in terms of optical output, luminous efficacy, and price, and their performance needs to be further improved. In particular, since current nitride semiconductor light emitting diodes still achieve low optical output as compared with existing white light sources, it is necessary to improve optical output and overcome thermal stability problems.
Meanwhile, a general nitride semiconductor light emitting diode is manufactured by forming a nitride n-type layer, a nitride active layer, and a nitride p-type layer on a sapphire substrate and horizontally disposing two electrodes to connect a power source to the n-type layer and the p-type layer. The horizontal light emitting diode can be manufactured by a relatively simple process and thus has an advantage of low manufacturing costs. However, the horizontal light emitting diode employs a sapphire substrate, which is nonconductive and has poor thermal conductivity, it requires application of a large area current for realization of a high output and suffers from low thermal stability due to accumulation of heat.
In order to overcome such drawbacks, a vertical semiconductor light emitting diode and a flip chip-type semiconductor light emitting diode have been suggested. In these diodes, a reflective layer is formed in a p-type electrode to allow light created by an active layer to be emitted to the outside through an n-type electrode, and a metal substrate having a good thermal conductivity is used instead of a sapphire substrate, thereby enabling application of a large area current and prompt discharge of heat to realize high output while securing thermal stability. Since vertical semiconductor light emitting diodes can achieve a maximum application current that is more than several times that of horizontal light emitting diodes, it is widely held that existing white light sources will be supplanted by high-output vertical semiconductor light emitting diodes in the future.
Meanwhile, it is necessary for an n-type electrode to have low resistance in order to improve operating voltage characteristics in a vertical semiconductor light emitting diode. For the vertical semiconductor light emitting diode, a metal substrate or a semiconductor substrate formed of Si, Ge, or the like is used and a sapphire substrate is removed through a laser lift-off (LLO) process, in which case high temperature heat treatment cannot be easily performed after the laser lift-off process due to a wafer bonding temperature and a large difference between thermal expansion coefficients of the metal substrate and the GaN thin film. Thus, Ti/Al n-type ohmic electrodes that can be formed at room temperature without any heat treatment have been widely used.
However, in the ohmic electrode, ohmic characteristics deteriorate due to heat generated upon heat treatment for forming a SiO2 protective film after formation of the electrodes or upon application of high current to a large area light emitting diode, thereby causing increase in operating voltage. Thus, there is an urgent need for an n-type ohmic electrode that exhibits low contact resistance after deposition while ensuring excellent thermal stability so as to maintain low contact resistance even after heat treatment.